Arc discharge lamp having reduced starting voltage

ABSTRACT

The arc tube of a metal halide arc discharge lamp contains a gaseous filling of about 60% argon - 40% neon.

Umted States Patent [191 BEST AVAILABLE COPY [111 3,895,251 Gungle etal. July 15, 1975 1 ARC DISCHARGE LAMP HAVING 3,577,029 5/1971 Koury etal. 313/229 REDUCED STARTING VOLTAGE 3,753,018 8/1973 Beijer et al.313/229 X [75] Inventors: W. Calvin Gungle Danvers, Mass.;

I Frederic Koury, Alexandria, NH. Primary Examiner Rl v. Rolinec [73]Asslgneez GTE Sylvania Incorporated, Assistant Examiner-Darwin R.Hostetter Danvers, Mass. Attorney, Agent, or Firm-James Theodosopoulos[22] Filed: Feb. 19, 1974 [21] Appl. No.: 443,347

[57] ABSTRACT [52] US. Cl 313/226; 313/229 [51] Int. Cl. H0lj 61/16 581Field of Search 313/226, 229 The arc tube of a metal hahde are dlschargelamp tains a gaseous filling of about 60% argon 40% [56] ReferencesCited neon UNITED STATES PATENTS 3,052,813 9/1962 Gungle et al. 313/229X 1 Claim, 1 Drawing Figure 13 27 26 E 26 25 I2 I I5 '1 ARC DISCHARGELAMP HAVING REDUCED STARTINGVOLTAGE BACKGROUND OF THE INVENTION 1. Fieldof the Invention r This invention relates to high intensity metal halidearc discharge lamps of the type used for general illumination. Suchlamps have a generally cylindrical arc tube having electrodes at eachend thereof. The arc tube contains a fill of mercury, metal halide and,for starting purposes, an ionizable gas. During normal operation, thepressure within the arc tube is between about one to ten atmospheres andthe arc tube temperature is between about 450 and 900C.

2. Description of the Prior Art Metal halide arc discharge lamps forgeneral illumination have become commercially useful in the past five toten years because they are more efficient and yield a whiter light thanhigh pressure mercury vapor lamps. The construction and operation ofmetal halide lamps are shown in the [ES Lighting Handbook, th ed. N-.Y.,Illuminating Engineering Society, 1972, p. 834.

The arc tube of such lamps contains an inert, ionizable gas for startingpurposes; the gas usually is argon.

It is known that mixtures of gases, so-called Penning mixtures, canreduce arc tube starting voltages to a lower value than that of singlecomponentgas fills. The reason for this is discussed in Waymouth, J. F.Electric Discharge Lamps. Cambridge. Mass. & London, England,'The M.I.T.Press, 1971, p. 63-67.

In a Penning mixture, one gas is present in a small quantity and theother gas is present in a larger quan tity, usually at least abouttwenty times the amount of the first ,gas. Examples of such mixtures areshown in us. Pat. Nos. 2,176,134 and 3,753,018.

SUMMARY OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWING The singleFIGURE in the drawing is an elevational view of a metal halide arcdischarge lamp in accordance with this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in the drawing, a metalhalide lamp in accordance with this invention includes a generallytubular outer bulbous envelope 1 having a bulbous central portion and aconventional base 14 attached to the bot tom thereof. Extending inwardlyfrom the base and inside of the envelope 1 is a mount 15 having a pairof stiff lead-in wires 12 and 16 in electrical conducting re lation withthe base 14. Disposed upon one of the stiff lead-in wires 12 is a lower,U-shaped support 8 welded thereto. U-shaped support 8 comprises a pairof vertical wires 23 and 24 rising from a horizontal base wire 25. Theupper ends of lower U-shaped support 8 are welded together with a lowerstrap 7 which in turn supports an arc tube 2. Preferably, the lowerstrap includes two sections abutting against either side of arc tube 2thereby holding it firmly in place. They touch only the press seal ofthe arc tube and not the body. Generally, both sides of the lower strap7 can be of identical construction. A pair of bumpers 26 are welded tolower U- shaped support 8 and abut against the tubular portion of thewalls of outer bulbous envelope 1, thereby stabilizing the structurewithin the lamp. Preferably, these bumpers are made of a resilientmaterial so that if the lamp is jarred they will absorb much of theshock.

Since lower U-shaped support 8 is electrically connected to stifflead-in wire 12, support 8 forms part of the circuit in the device.Current passes from base 14 into lower U-shaped support 8 and thence tolead-in wire 21 which in turn is connected to electrode 4 in the arctube. It is sometimes desirable to place an insulating shield aboutlead-in wire 21 to prevent arcing within the lamp and between thevarious elements. Current passes from lead-in wire 21 to electrode 4through an intermediary molybdenum 'foil section 6.

The other side of the circuit is formed through stiff lead-in wire 16which is preferably bent out of place so that parts on one side of theline are insulated from those on the other side. A resistor 13 isattached to' stiff lead-in wire 16 through a lead-in wire associatedtherewith and thence to a connector 27 which in turn leads through amolybdenum foil secton 6 to a starting probe 5. A bimetal 22 is disposedbetween lead-in wire 21 at; tached to electrode 4 and connector 27 whichis attached to starting probe 5. Bimetal 22 is biased open when the lampis turned off but when the lamp starts, it biases closed against thelead-in wires to probe 5 thereby establishing the same electricalpotential at probe 5 and electrode 4. Such closing prevents electrolysisbetween the probe and electrode.

At the other end of arc tube 2, an upper support 10 is mounted withinthe tubular portion of bulbous envelope 1. Support frame 10 includes ahorizontal section 18 having vertical supports 17 and 19 dependingdownwardly therefrom and attached at the free ends to an upper strap 11which surrounds the press seal of arc tube 2 and rigidly holds it inplace. Preferably, the con struction and deposition of upper strap 11 issimilar to lower strap 7. A pair of upper bumpers 9 are mounted uponvertical sections 17 and 19 of upper support 10 and resiliently abutagainst the sides of the tubular portion of bulbous envelope 1. Suchdisposition prevents breakage of the arc tube if the lamp is shaken ordropped.

A lead-in wire 28 extends to the outside of arc tube 2 and is attachedat its inner end to a molybdenum foil section 6 and thence to electrode3. An electrical connection is made between stiff lead-in wire 16 andleadin wire 28 through a thin conducting lead 20 which may be of anysuitable conducting material. Preferably, conducting lead 20 isdistantly removed from arc tube 2, generally by bending it close to theperimeter of outer bulbous envelope 1.

Disposed within arc tube 2 is an inert starting gas mixture of neon andargon, and a fill which includes mercury, halogen and a light emittingmetal. The light emitting metal can be one or more of scandium, sodium,thorium, thallium, indium or any light emitting metal commonly used inmetal halide lamps and can be added in element or compound form. Thehalogen,

The starting gas mixture of neon and-argonis outside 7 the compositionof a Penning mixture and is, preferably, for minimum starting voltage.about 60% argon and 40% neon.

Starting voltage was determined for 400 watt metal halide arc dischargelamps containing a fill of mercury, sodium iodide and scandium iodideand containing a starting gas filling at 35 torr of various mixtures ofneon and argon. For lamps at room temperature, starting voltage atmixtures of 100% argon, 80% argon-20% neon, 60% argon-40% neon, 40%argon-60% neon, 20% argon-80% neon and 100% neon were, respectively, 315volts, 290 volts, 245 volts, 295 volts, 300 volts and 260 volts, using asine wave reactor. At 20F, using a ballast, the starting voltages forthe same mixtures were, respectively, 270 volts, 250 volts, 235 volts,265 volts, 345 volts and 335 volts. In both cases, the lowest startingvoltage occurred at a gas composition of about 60% argon-40% neon.

An advantage of this invention lies in the fact that it permits use ofhigher gas fill pressures than are normally used in metal halide lamps,without significant increase in starting voltage. Higher gas fillpressures are desirable since they improve lamp maintenance by reducingelectrode sputtering during lamp warm-up. The change in starting voltageversus gas fill pressure was as follows: for argon fill alone, roomtemperature starting voltage was 257 volts at 35 torr and 270 volts at50 torr. In contrast, for 60% argon-40% neon, starting voltage was 260volts at 35 torr but decreased to 250 volts at 50 torr. Similarly, at-20F., starting voltage for argon alone was 300 volts at 35 torr andincreased to 343 volts at 50 torr; for 60% argon-40% neon, startingvoltage was 293 volts at 35 torr and only 295 volts at 50 torr.

The improvement in starting voltage continued throughout the life of thelamps. For example, after 6400 hours of operation, the average startingvoltage for prior art lamps, which had a gas fill of argon at 35 torr,was 27] volts. In contrast, the starting voltage for lamps in accordancewith this invention after 6400 hours of operation was lower, even at gasfill pressures as high as 80 torr. The results were as follows: for gasfill of 60% argon-40% neon at 50 torr, average starting V was 263 volts.

Another advantage of the gas fill of this invention results from thelower quantity ofneon of neon the arc tube gas fill mixture as comparedwith the quantity of neon in a Penning mixture. As mentioned in thepreviously cited U.S. Pat. Nos. 2,176,134 and 3,753,018, neon candiffuse through the walls of arc tube 2, thus requiring the filling ofouter envelope 1 at least partially with neon. But neon has a higherheat conductivity than other gases, such as nitrogen, normally used inthe outer envelope and can thus lower lamp efficiency by cooling the arctube more than said other gases. The lower neon content of the gasmixture of this invention requires less neon in the filling of outerenvelope 1.

We claim:

1. A high intensity metal halide arc discharge lamp comprising a sealedarc tube having electrodes at each end thereof and containing a fillincluding mercury, metal halide and a starting gas filling, said fillingcomprising a mixture of about 60% argon-40% neon.

1. A HIGH INTENSITY METAL HALIDE ARC DISCHARGE LAMP COMPRISING A SEALEDARC TUBE HAVING ELECTRODES AT EACH END THEREOF AND CONTAINING A FILLINCLUDING MERCURY, METAL HALIDE AND A STARTING GAS FILLING, SAID FILLINGCOMPRISING A MIXTURE OF ABOUT 60% ARGON-40% NEON.